Motor speed control



July 3, 1951 H. s. JACOBS 2,559,538

MOTOR SPEED CONTROL 2 Sheets-Sheet 1 Filed April 16, 1945 I INVENTOR. Mfj k 44 b ATTORNEY July 3, 1951 I H- s. JACOBS 2,559,538

MOTOR SPEED CONTROL Filed April 16. 1945 '2 Sheets-Sheet 2 94 f z 9/ zldbiiiiym' 1 III:

INVENTOR.

A TTORNEY Patented July 3, 1951 MOTOR SPEED CONTROL Henry S. Jacobs, Milwaukee, Wis., assignor to Hamischfcger Corporation, Milwaukee, Wis, a corporation of Wisconsin Application April 16, 1945, Serial No. 588,685 Claims. (Cl. 318-141) Thlsinvention relates to electric motor 00D? trol of the type wherein the motor remains permanently connected to a generator whose output is varied by regulation of the excitation of the generator field, and it resides more specifically in a system of this general character wherein field excitation of the generator (and the motor also, if desired) is in part atleast created through regulated application of alternating current to rectifiers the outputs of which are applied in turn to field windings. In its preferred form regulation of the alternating currents utilized is accomplished through alterations in magnetic flux paths rather than through alterations in electrical circuit connections and in this way motor control is accomplished entirely without resort to electrical switching. In a further extension of the principle of this invention speed regulation of a motor independently of regulation of a generator is also contemplated.

In the well known variable voltage motor control of the type usually designated Ward Leonard, a generator having field windings .which may be variably excited is employed. By

arranging for reversal of excitation as well as its modulation and by employing a motor with a separately excited field, reversal of the motor as well as regulation of its output may be accomplished by control of the generator alone. In cases where the motor is subjected to highly variable and unpredictable loads, such for example as occur in the driving of certain elements of excavating machines, self protecting characteristics must be incorporated in the generator. In meeting this requirement a somewhat elaborate generator field system must be resorted to thus necessitating a complex switching arrangement for bringing about the several control functions desired. In equipment of large capacity the field currents to be controlled may be of such magnitude as to require an undesirably large amount of expensive switching equipment. The seriousness of the difliculty has led at times to the employment of a multiplicity of separate exciting generators whose smaller field currents may in turn be regulated by switching arrangements of more moderate size and expense. An-

other attempt to cope with the problem resorts,

to a specially designed generator capable of operating with exceptionally low field currents so that the switching problem is simplified. In all of these, the need for switching is not eliminated but is merely rendered less exacting so that available equipment may more nearly cope with the requirements.

In accordance with the present invention a system of variable voltage motor control is provided which may dispense entirely with circuit switch ing means. This is accomplished by supplying the necessary excitation currents for the generator field windings through rectifiers which are supplied in turn with alternating current which may be inductively or reactively regulated to the intensity desired, or in the case of independent motor control by regulation of the motor circuits alone in this fashion. Inductive or reactive regulation of the alternating current supply is accomplished without the opening, closing or altering of any circuit connection and in this way all need for switching is eliminated.

If for any reason it is desired to produce regu lation of the alternating current supply by switching rather than inductively or reactively, the same may be resorted to as a limited application of this invention. In this case certain advantages other than the advantage of switchless regulation are nevertheless preserved in certain cases.

Among the advantages in addition to switchless regulation which the system of this invention exhibits, where a generator-motor system is controlled, is the advantage that the predominant generator field windings are of a unidirectional character giving to the operator positive control of generator polarity. All systems heretofore in use depend upon predominant field windings Whose polarity must be reversed in order to cause reversal of the motor under control. Since a differential series field and a self excited cumulative shunt winding in addition to a separately excited field are essential parts of such systems a very annoying and possibly dangerous property is exhibited when an eifort is made to plug suddenly while the motor is operating at high speed. Due to back voltage of the motor armature under such a condition the series winding becomes cumulative rather than differential in its effect adding to the efiect of the self excited shunt field with the result that the separately excited field is not able to dominate and reverse the polarity of the generator. As a result the motor continues to drift for a prolonged interval at the very time the most abrupt stoppage possible is being demanded by the operator. Because of this possibility the tendency has been to limit the strength of the self excited shunt field and to strengthen the separately excited field so that its predominance will be insured under all conditions. When this inclination is followed to the point where the difliculty in question is overcome,- rapid accelerationof the motor is sacrifled. An eifort is, therefore, usually made to strike a compromise with the result that both disadvantages are usually present to a considerable degree, that is, some tendency to refuse to plug immediately at high speed still persists and acceleration is deficient. With the positive control of unidirectional field windings employed with the present invention no compromise is necessary. Plugging with substantial reverse torque and without undue delay, and rapid acceleration can both be made available in one and the same machine.

A further advantage of this invention is its inherent rapid but smooth modulation of control and load transitions. This advantage is possessed by reason of the permanent connection of certain field windings to unidirectionally conducting circuit elements of the rectifiers. By reason of this the field windings exhibit high self inductance on certain occasions and low self inductance on other occasions in a manner beneficial to the performance of the apparatus as a whole.

This invention is herein described by reference to the accompanying drawings forming a part hereof and in which there is set forth by way of illustration and not of limitation certain forms in which this invention may be embodied.

In the drawings:

Fig. l is a diagram showing one form of the electrical circuit of this invention;

Fig. 2 is a diagram of a fragment of a circuit showing a different type of motor field arrangement, which may be substituted for the motor field arrangement of Fig. 1;

Fig. 3 is a diagram of a circuit arrangement by which speed control of an alternating current motor may be obtained in accordance with this invention.

Referring to Fig. 1 of the drawings a generator field frame I having pole pieces 2, 3, 4 and 5, surrounding an armature 6 is diagrammatically depicted. The armature 6 is mounted to be driven in customary manner by means not shown and is wound in conventional fashion and connected to a commutator 'I. In addition to the commutator 1 armature carries a pair of slip rings 8 and 9, the same also being connected to the armature winding in known manner so as to receive alternating current therefrom. A set of brushes ll mounted to engage commutator l is connected on the one hand through differential series field windings ll, l2, l3 and i4 and lead H8 with an output terminal 15, and on the other hand by a lead with an output terminal ll. The differential series field windings H, l2, l3 and i4 perform a useful adjunctive function in the particular form of the apparatus shown as will be more fully explained hereinafter. Such windings, however, are not essential to the main purposes to be accomplished and may be dispensed with or may be supplanted by other means productive of a similar regulating effect such as arrangements adapted to accentuate the effect of armature reaction as disclosed in my co-pending application Serial No. 561,098 filed October 30, 1944, now Patent Number 2,475,175, patented July 5, 1949, for Power Transmissions.

In the particular form of the apparatus shown it is intended that only two pole pieces be directly excited at one time, the other pole pieces being left to be indirectly excited by magnetic induction as consequent poles. In the case of pole pieces 2 and 4 the same are arranged to be simul- 4 taneously excited directly by externally supplied windings l8 and 20 and by internally supplied windings 22 and 24. Windings l8 and 20 are joined by a lead 26 and the outer ends of the two windings thus joined are connected by leads 21 and 28 with leads 29 and 30 joined respectively with the output terminals 3| and 32 of a full wave rectifier 33. Rectifier 33 is provided with input terminals 34 and 35 the same being joined respectively by leads 36 and 31 with the ends of a secondary winding 38 which surrounds a stationary secondary leg 39 of an induction regulator designated generally by the numeral 4|.

Induction regulator 41 is made up of a rectangular frame 40, hearing a divided primary winding 43, a movable flux deflecting regulatin arm 44, the secondary leg 38 previously mentioned, a similar stationary secondary leg 42 hearing a, secondary winding 45, and an intermediate stationary by-pass leg 46. The ends of the primary winding 43 are connected by leads 41 and 48 with alternating current supply leads 49 and 59. The movable regulating arm 44 is pivotally mounted by means not shown and provided with a regulating handle 5| by which it may be moved to and held in any position desired between the position in which it is shown and its opposite position indicated by dotted lines.

When the regulating arm 44 is in the position shown, the transformer action between the primary winding 43 and the secondary winding 38 is such that alternating current is supplied by the winding 38 to the rectifier 33 at maximum potential. As the regulator 44 is moved toward the by-pass leg 45, the potential of the alternating current supplied by winding 38 to the rectifier 33 is gradually diminished to substantially zero. Further movement of the regulator 44 toward the leg 42 causes an increasing potential to be established in winding 45.

Alternating current supplied to the rectifier 33, results in the establishment of a direct current potential at rectifier terminals 3| and 32 and as a consequence exciting current is caused to flow unidirectionally in the externally excited field windings l8 and 29. The flux thus established in the generator field and armature structure (assuming armature 6 to be turning) results in the generation of electrical potential in the windings of armature 6. This potential appearing as an alternating potential at the slip rings 8 and 9 is picked up by brushes 52 and 53 and by them applied to leads 54 and 55.

Leads 54 and 55 are joined as shown with leads 55 and 51 which extends toward the left to connect respectively with terminal 58 of a reactor bridge 6! and input terminal 59 of a full wave rectifier 60. Reactor bridge BI is made up of a three legged magnetic frame 62 having sections of a divided impedance winding 63 surrounding its two outer legs. One end of the winding 63 joins with the terminal 58 while the other end is joined to a lead 65 by a terminal 64. Lead 65 is connected in turn to the other input terminal 56 of the rectifier 60. The central leg of reactor BI is surrounded by a saturation winding 61 which is joined by the terminals 68 and'69 with leads 29 and 39 for a purpose to be presently described.

Rectifier 60 is provided with output terminals Ill and H the former being connected by lead 12 with one end of self excited field winding 22 and the latter being connected by a lead I3 with one end of field winding 24. Windings 22 and 24 are joined by a lead 14 and thus caused to be assasas simultaneously excited by current supplied by the rectifier 30.

Since the source of the rectified electrical en-' ergy supplied to the winds 22 and 24 is derived from the alternating current output of the armature 8 the intensity of the-samewill be proportional to the direct current voltage also supplied by the armature 6. The intensity of this excitation is furthermore dependent upon the impedance offered by'the saturation controlled reactor OI. The impedance of the winding 83 of reactor 8| is subject to being varied and controlled by the degree of saturation of the magnetic frame 82 and this is subject to alteration through variations in the magnitude of the current flowing in a saturation winding 61. When induction regulator 4| is adjusted to cause the output of rectifier 33 to be at a maximum so also will the degree of saturation of frame 92 of the reactor 9| be at a maximum, and as a consequence a minimum of impedance to current fiow will be offered by the winding 63 under that condition. The degree of excitation of windings 22 and 24 is therefore a function of both the voltage of armature and the position of regulator 4|.

Reactor 6| is preferably proportioned and wound to provide a maximum impedance sufficient to nearly stifie the excitation of windings 22 and 24 whenever the regulator 4| is in mid position. In this way a positively controlled self excited winding is provided in which termination of excitation is not dependent upon conditions prevailing within the generator. Windings I8 and 20 and windings 22 and 24 are arranged in the apparatus as shown to act accumulatively, for the purpose of producing a suitable build up of motor accelerating voltage.

In order to produce reverse fiux in the field of the generator for the purpose of reversing the current output thereof, pole pieces 3 and are arranged to be directly excited in such a direction as to reverse the flux through armature 6 and to cause pole pieces 2 and 4 to be rendered consequent poles by reason of induced magnetism. For this purpose pole pieces 3 and 5 are provided with externally excited windings I9 and 2|, joined by a lead 15 and connected at their outer ends by leads 16 and 11 with the output terminals of a rectifier 18 which in turn is arranged to be supplied by winding 45 of induction regulator 4|. Pole pieces 3 and 5 are further provided with internally excited windings 23 and 25 which are joined by a lead 19 and connected at their outer ends by leads 80 and 8| with the output terminals of a rectifier 82. Rectifier 92 is connected by lead 83 and saturation reactor 84 with lead 58 on the one hand and is directly joined with lead 51 on the other hand and in this way is arranged to be supplied with alternating current from the armature 6. The saturation winding 95 of reactor 84 is connected by leads 88 and 91 with the output of rectifier 18.

It will be observed that pole pieces 3 and 5 are th us subject to excitation and control in exactly the same manner as pole pieces 2 and 4 but alternatively with the same and in such direction as to reverse the flux through the armature 8. The output of the generator thus can be regulated by manipulation of handle 5| so as to alter the magnitude or the polarity thereof at will and entirely without the opening or closing of any switch. This action is herein referred to as switchless regulation.

The current supplied at the generator terminals I5 and I1 is caused to fiow through pera lead 91 and connected at its outer end by leads 98 and 99 with direct current power lines I00 and IN. Motor 9| mayvalso be provided with a differential field winding I02, I03 joined by a lead I04 and connected at its outer end by leads I and I08 with the output terminals of a rectifier I01. One input terminal of rectifier I01 is connected by a lead I08 with alternating current power supply line 49. The other input terminal of rectifier I01 is connected by a lead I09, impedance winding 0 of reactor 94 and lead III with the other alternating current supply line 50.

Since the direction of field excitation of motor 9| is independent of the direction of motor armature current and remains unchanged, reversal of motor 9| can be caused simply by reversal of generator output which is under control of handle 5|. While the direction of motor field excitation is independent of armature current the intensity thereof is not. As motor armature current increases so also does the strength of the bucking windings I02 and I03 by reason of the greater saturation and therefore smaller impedance prevailing inreactor 94. Thus, the net field flux of motor 9| may be caused, to behave much in the manner of a differential series separately excited shunt motor but with the unique advantage of full reversibility by simple reversal of armature current. As a result a more adaptable power transmission having greater aptitude of self adjustment to rapidly varying load conditions is provided.

In certain cases it may beadvantageous to employ a motor somewhat different from the motor 9|. For example, in Fig. 2 is shown a motor 9| having a difierent field arrangement which may be substituted for the motor 9| shown in Fig. 1. In this case, a single field winding composed of coils I02 and I03 is arranged to be supplied by a rectifier I01 which in turn is supplied with alternating current controlled by passage through the impedance winding N0 of a saturation reactor 94'. As in the case of the motor 9| shown in Fig. 1, the main armature current is caused to pass through a saturation winding 93'.

The winding III) of the saturation reactor 94' is so proportioned that with no direct current passing through winding 93 a small but substantial fraction of the rated field current of the motor 9| is permitted to pass. The magnitude of thisfraction will depend upon the service to be performed, but in certain specific instances I prefer an arrangement which will supply from 20 to 30 per cent of the maximum field current under the condition mentioned. As the main armature current increases through the winding 93' the current passing through the field windings I02 and I03 will increase accordingly, reaching a maximum when armature current is at a maximum.

In the arrangement shown in Fig. 2 as soon as the control is thrown into the full-on position, and before motor 9| actually begins to rotate, a maximum stalled motor current is permitted to flow in the armature circuit. Under these conditions the saturation coil 93' on the saturation reactor 94 receives its maximum excitation, thus permitting the maximum current cause to flow through the winding the rectifier I01 and the motor field windings I02 and I03. This produces a field condition closely parallel to that prevailing in a series or heavily compound wound motor. As motor 9| accelerates, the main armature current falls off and the saturation reactor 94' causes a diminution in the field current supplied to the windings I02 and I03. Motor 9| is therefore caused to operate in a manner quite similar to a heavily compounded or series motor under this condition also. An additional advantage of the motor shown in Fig. 2 is that it is capable of very rapid deceleration during plugging, due to the fact that the motor field actually increases as motor speed falls off. The motor further has a higher ultimate speed and is capable under conditions prevailing in excavator operation of performing close to the peak of its power curve during a larger part of its duty.

The motor shown in Fig. 2, of course, has the same advantage as the motor shown in Fig. l in that it may be plugged and reversed by simple reversal of armature current.

While sudden shifting of controller handle 5I from full forward to full reverse with motors 9I or 9| running under light load and at high speed will positively plug and reverse the same, this action cannot occur with such abruptness as to give rise to undesirable mechanical and electrical shocks in the system, Smooth and moderate transitions are caused in the apparatus of this invention by certain inherent self induction actions. For example, if the handle 5i is suddenly shifted from the position shown, the collapsing field in pole pieces 2 and 4 is delayed momentarily by a substantially between windings 20, I8 and rectifier 33 and similarly between windings 23, 24 and rectifier 59. This follows since the unidirectional conductivity of the rectifiers 33 and 59 is correctly orientated to produce the desired efiect.

Further, upon the bringing of member 44 suddenly into registry with leg 42, immediate excitation of pole pieces 3 and 5 is momentarily delayed by impedance of windings I9, El, 05, 23 and 25. In addition, the building of flux in pole pieces 2 and 4 as consequent poles sets up induced currents in windings I8, 20 and 22, 20 which find low resistance paths through their respective rectifier thus adding further to the self induction available to soften the effect of sudden excitation.

The identical actions in reverse take place upon sudden displacement of the handle III in the other direction.

While, as explained above, switchless regulation is of great advantage particularly in the case of larger apparatuses, substitution of switches for the regulator 4| and the reactors GI, 04 and 94 or any of them may be resorted to ii desired. The positiveness of field control without need for sacrificing acceleration and other advantages would be retained even though switchless regulation were dispensed with.

In its preferred form, as now shown, rectifiers 33, 18, 59, 02 and I01 are of the well known dry disk type having as an active material either selenium oxide or copper oxide. This invention, however, is independent of the particular form of rectifier employed, since electron emission or ionized gas or vapor rectifiers or rectifiers of other types may be used either in full wave or the partial wave form.

This invention may also be applied to the conclosed circuit condition trol of alternating current motors. One manner of thus applying the invention is illustrated in Fig. 3 where a conventional three phase slip ring induction motor I01 having a stator H2 and a wound rotor H3 is shown. Power for operating the motor I81 is supplied through power mains H4, H5 and H6.

Terminal II1 of motor III is connected by a lead II8 with a connecting lead III! which joins the ends of reactor windings I20 and I2I mounted respectively upon saturation reactors I22 and I23. The opposite ends of windings I20 and I2I are joined by leads I24 and I25 with mains H4 and H6 respectively. In this way two alternative admission paths for supplying current to the terminal II1 are provided making it possible to establish the equivalent of direct connection from main H4 or III; with the terminal II1.

In similar fashion terminal I26 is connected by lead I21 with a connecting lead I28 joining the ends of reactor windings I29 and I30 mounted respectively upon saturation reactors I3I and I32. The opposite ends of windings I29 and I30 are joined respectively by leads I33 and I34 with mains H6 and H4 respectively. In this way alternative admission paths between mains H6 and H4 and the terminal I26 are provided.

Terminal I35 of motor I01 is connected by lead I36 to a connecting lead I31 joining the windings I38 and I39 on saturation reactors I40 and MI respectively. The opposite ends of windings I38 and I39 are joined together by lead I42 which is in turn connected by lead I43 with power main I I5. While two admission paths are thus provided for the terminal I35 of motor I81, the same are not alternative and are confined to a single connection with main I I5 for purposes to be more fully described hereinafter.

Saturation reactors I23, MI and- I32 are arranged to be controlled by saturation coils I44, I45 and I46, the same being connected in series and joined at one end by means of lead I41 with one output terminal of a rectifier I48. Rectifier I40 is arranged to be supplied with alternating current by an induction regulator winding I49 joined thereto by leads I50 and I5I.

The winding I49 forms a part of an induction regulator I52 having an input winding I53 joined by leads I54 and I55 with power mains H6 and II4. Induction regulator I52 also has another output winding I56 which is joined by leads I51 and I58 with the input terminals of a rectifier I59.

Saturation reactors I22, I40 and I3I are com trolled by saturation windings I60, I6I and I62 which are connected in series and joined by lead I63 with one output terminal of rectifier I59. The return connection for the saturation windings of the saturation reactors is provided in a manner to be presently described.

In addition to the regulating means above dcscribed and associated in circuit with the primary or stator windings regulating elements in circuit with the secondary or rotor windings may also be employed as illustrated. Connected respectively with slip ring terminals I64, I65 and I66 are secondary resistors I61, I68 and I69 respectively. The resistors I61, I68 and I69 are joined at their outer ends by leads I10 and Ill. In shunt relationship with resistors I61, I68 and I69 are impedance windings I12, I13 and I14 respectively, the same being mounted upon and as part of saturation reactors I15, I16 and I11.

Saturation reactors I15, I16 and I11 are provided with saturation windings I18, I19 and I80. Saturation windings I18, I19 and I are means oflead I8I. and leads.l82 and I83 with the lower ends of windings I46 and I62 respectively. In this way windings I18, I19 and I88 provide a return connection for all of the other saturator windings devoted to the control of the primary circuit, this being accomplished by the return lead I84 which joins at one end with the winding I88 and at the opposite end with a cross connecting lead I85 which is connected as shown to output terminals of rectifiers I "and I59. By reason of the unidirectional conductivity of the said rectifiers a single return lead I84 is sufiicient for the purpose as will be more fully explained hereinafter.

In normal operation at the outset the fiux diverting arm I86 of induction regulator I52 will be in mid or vertical position and neither of the windings I49 nor I66 will be excited. If the operator chooses to deflect the arm I86 to the position shown in the drawing winding I48 becomes excited and rectifier I48 becomes a source of direct current potential. When this occurs, saturation reactors I23, I, I32, I15, I16 and I11 become saturated and their corresponding reactor coils are deprived of their normally high impedance. This permits power to be admitted from mains H4, H and H6 to terminals II1, I35 and I26 respectively. The motor III being thus supplied with power tends to accelerate. At the outset of this acceleration there is little impedance in the windings I12, I13 and I14 by reason of the more or less complete saturation o the magnetic material with which they are associated. Large secondary currents are thus permitted to fiow to provide a large starting torque if desired and motor III accelerates and behaves in a manner comparable to that of a squirrel cage motor. If the arm I86 of the induction regulator I52 were thrown to the extreme opposite position, an entirely comparable situation would exist except that the motor III would be driven in the opposite direction. Complete reversability of motor II without 'resort to any switching is thus provided.v

If regulation of the output of motor III is desired, the arm I86 is moved to an appropriate intermediate position between its mid position and the position shown. .When this occurs, incomplete saturation of saturation reactors I23, I4I, I32, I15, I16 and I11 is provided, and their corresponding reactor coils exhibit a corresponding impedance. placed upon the voltage applied to the primary windings of motor III and furthermore at the outset of acceleration interposes an equivalent resistance in the secondary circuit somewhat less than the resistance of resistors I61, I68 and I69. As acceleration of motor III progresses, the frequency of secondary current diminishes and without any alteration of the position of arm I86 the efiect of secondary resistance diminishes accordingly. This permits the starting of motor III with a moderate 'inrush of starting current and furthermore permits speed regulation of motor I I I steplessly over a wide range.

Saturation reactors I40 and I, while not essential to the main objective to be accomplished, serve to maintain complete balance in the primary circuit of motor III throughout the range of regulation of power input. They play no part, however, in the reversibility function which is Joined in series and connected, at one end by v with the regulating circuit, elements in the secondary circuit and to employ, if desired, agsquirrel This causes a limitation to be performed entirely by saturation reactors I22 and I3I on the one hand and I23 and I32 on the opposite hand. It is also possible to dispense cage rotor in place of the wound rotor II3. In such an arrangement complete reversibility is preserved and some measure of speed control might also be obtained depending upon the character of the load imposed upon the motor I I I.

The secondary circuit of the apparatus shown in Fig. 3 may also be re-arranged to cooperate with other well known speed regulating arrangements, such as. cascading or concatenation arrangements either direct or differential or both. For example, if the resistors I61, I68 and I69 are replaced by or regardedas being the stator windings of a squirrel cage motor, the shaft of which is mechanically coupled with the shaft upon which rotor I I3is mounted, then a cascading system is established which calls for full speed operation when saturation reactors I16, I16 and I11 are excited and half speed operation when the same are not excited. With such an arrangement it may be'desirable to control the excitation of saturation reactors I15, I16 and I11 independently or semi-independently of the control of saturation reactors I44, I45, I46 and I60, I6I, I62. This can be easily accomplished by providing an additional variably supplied rectifier for furnishing excitation current to the saturation reactors I15, I16 and I11. In like manner other variable speed motor arrangements such as the spinner. type motor having an intermediate rotor may be steplessly regulated without resort to switches by application of the invention herein disclosed.

I claim:

1. In a dynamoelectric machine an armature and field frame including pole pieces forming a flux path; a first field winding therefor adapted to establish fiux in said path in one direction; a second field winding therefor adapted to establish flux in said path in the opposite direction; an induction regulator having a primary winding adapted to be connected to a source of alternating current, a first and a second secondary winding and means for controllably and selectively vary-, ing the magnetic coupling between said primary winding and said secondary windings alternae tively and to the mutual exclusion of one another; a first rectifier connected to be supplied with alternating current delivered by said first secondary winding; means forming a circuit connection between said first rectifier and said first field winding for applying the unidirectional out put of said rectifier to said field winding; a second rectifier connected to be supplied with alternating current delivered by said second secondary winding; and means forming a circuit connection ,between said second rectifier and said second field winding for applying the unidirectional output of said rectifier to said fieldwinding.

2. In a dynamoelectric machine an armature and a field frame including pole pieces forming a fiux path; an externally excited field winding; means adapted to be connected to an external source of alternating current including a rectifier connected to said externally excited field winding for supplying unidirectional current thereto, means associated with said armature adapted to generate alternating current; a self excited field winding; a second rectifier means adapted to connect said armature alternating current output to said rectifier and through said rectifier with said self excited field winding, and v a variable reactance interposed between said armature and said second rectifier adapted to control the current delivered thereto, and circuit means associated with said first rectifier and said variable reactance adapted to vary the impedance of the latter in response to the output potential of said first rectifier.

3. In a dynamoelectric machine an armature, a field frame, a first and second set of pole pieces adapted to be excited as directly excited pole and alternatively to be excited as consequently excited poles, forward windings adapted to excite said first set of poles directly and the remainder of said poles as consequent poles to establish a forward fiux path, reverse windings for exciting the second set of said poles directly and the remainder of said poles as consequent poles to establish a reverse flux path, a source of alternating current, a first rectifier connected to be supplied by said alternating current source and connected to said forward windings to supply direct current thereto, a, first inductively regulated means for varying the strength of alternating current supplied by said alternating current source to said rectifier, a second rectifier connected to be supplied by said alternating current source and connected to said reverse windings to supply direct current thereto, and a second inductively regulated means for varying the strength of alternating current supplied by said alternating current source to said second rectifier.

4. In an electrical apparatus adapted to transmit mechanical power reversibly the combination comprising a generator adapted to be driven by a unidirectional prime mover, a motor electrically connected to said generator to be driven thereby, separate forward and reverse field windings for said generator for reversing the polarity of the output thereof, means for energizing said generator field windings separately and alternatively, a saturation reactor having a saturation winding in circuit with said electrical connections joining said generator and said motor and an impedance winding, a rectifier in circuit with said impedance winding adapted to be supplied by alternating current passing therethrough, a separately excited field winding for said motor, and circuit connections joining said motor field winding with the direct current output of said rectifier.

5. In a dynamoelectric machine the combine- 12 tion comprising a field frame having pole pieces, an armature having windings, slip rings and brushes connected to said armature to receive alternating current therefrom, a saturation reactor having an impedance winding and a saturation winding, a first rectifier in circuit with said slip ring brushes and said impedance winding tobe supplied with alternating current therefrom and passing therethrough, a second rectifier having its output in circuit with said saturation winding, means for supplying a controllable alternating current to the input of said second rectifier, a first field winding on said pole pieces, means forming a circuit connection between the output of said first named rectifier and said first named field winding, a second field winding on said pole pieces and means forming a circuit connection between the same and the output of said second named rectifier.

HENRY S. JACOBS.

REFERENCES CITED The following references are of record in the file of this patent:

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